类型错误：无法读取未定义的属性“国家/地区”

Question

我正在尝试从 API 获取数据并在我的应用程序中使用该数据。但问题是，当我尝试从刚刚从 API 获取的 JSON 中获取某些对象或数据时，我得到：

类型错误：无法读取未定义的属性“国家/地区”。

属性

DO 存在。 顺便说一句，我正在使用 React.js。
我非常感谢您的帮助和指导。
这是代码：

应用程序.js

import React, {useEffect, useState} from 'react';
import './App.css';
import Navigation from "./components/Navigation/Navigation";
import Forecast from "./components/forecast/forecast";
// function

class App extends React.Component {
    constructor(props) {
        super(props);
        this.state = {
            responseFromAPI: {},
        }
    }

    getPosition = function () {
        return new Promise(function (resolve, reject) {
            navigator.geolocation.getCurrentPosition(resolve, reject);
        });
    }
    getWeather = async function (latitude, longtitude) {
        const One_weather_call = await fetch(`https://community-open-weather-map.p.rapidapi.com/weather?lat=${latitude}&lon=${longtitude}&units=metric`,
            {
                "method": "GET",
                "headers": {
                    "x-rapidapi-host": "some private info here",
                    "x-rapidapi-key": "some private info here"
                }
            }).then(response => response.json());

        console.log("fetch data");
        return One_weather_call;

    };

    componentDidMount() {
        this.getPosition()
            .then(position => {
                this.getWeather(position.coords.latitude, position.coords.longitude)
                    .then(res => {this.setState({responseFromAPI: res});
                    });
            });

        console.log("after setting response in app.js ", this.state.responseFromAPI);


    };

    render() {
        return (
            <React.Fragment>
                <Navigation city={this.state.responseFromAPI.name}

                            country={this.state.responseFromAPI.sys.country}
                />

            </React.Fragment>
        );
    };
}

export default App;

JSON

{"coord": { "lon": 139,"lat": 35},
  "weather": [
    {
      "id": 800,
      "main": "Clear",
      "description": "clear sky",
      "icon": "01n"
    }
  ],
  "base": "stations",
  "main": {
    "temp": 281.52,
    "feels_like": 278.99,
    "temp_min": 280.15,
    "temp_max": 283.71,
    "pressure": 1016,
    "humidity": 93
  },
  "wind": {
    "speed": 0.47,
    "deg": 107.538
  },
  "clouds": {
    "all": 2
  },
  "dt": 1560350192,
  "sys": {
    "type": 3,
    "id": 2019346,
    "message": 0.0065,
    "country": "JP",
    "sunrise": 1560281377,
    "sunset": 1560333478
  },
  "timezone": 32400,
  "id": 1851632,
  "name": "Shuzenji",
  "cod": 200
}

如您所见，这个 JSON 数据中的国家/地区的放置方式如下

json.sys.country

但是我这样得到错误。但是当我尝试访问其他变量（例如

json.main

）时没有错误。

Answer 1

最后，我通过有条件地设置

render()

 函数中组件的 props 来解决问题，如下所示：

  render() {
        return (
            <React.Fragment>

                <Navigation city={this.state.responseFromAPI ? this.state.responseFromAPI.name : ""}

                            country={this.state.responseFromAPI ? this.state.responseFromAPI.sys.country
                            : "Loading"}
                />

            </React.Fragment>
        );
    };